The present invention is a method and apparatus for the sonographic guidance and visualization of a catheter tip. The present invention includes both a device which is capable of coupling acoustic energy into optical fibers and a novel method of localizing the distal end of those fibers.
During a surgical operation, it may be necessary to insert a catheter or needle into a patient to perform a biopsy or to provide aspiration or drainage. The surgeon must know the exact location of this probe within the body. The visualization of the probe location is accomplished by directing ultrasonic energy into the patient and then by detecting the ultrasound reflections that bounce off of the catheter or needle. Over the past few decades, surgeons have relied upon the echogenic characteristics of the materials used to fabricate catheters and surgical needles to visualize the location of such a probe in the body or in a blood vessel. The echogenecity of a needle may be enhanced by roughening the outer surface of the needle or by applying a suitable coating. The reflectivity of these probes may also be improved by decreasing their diameter or by injecting air or water through their centers. These methods of achieving better echogenecity, however, are accompanied by serious limitations. As an example, scoring a needle does optimize its ability to produce ultrasound echoes, but the scoring also reduces the needle's strength.
Other previous attempts to enhance the surgeon's ability to visualize the tip of a probe or needle within the patient have included the use of an active device placed at the tip of the catheter. This modified catheter encloses a metal wire which conducts electrical energy from an outside source to its remote or distal end inside the body. The remote end of the catheter has an active ultrasonic transducer attached to its tip that emits acoustic energy. This energy is received by a sensor placed on the skin of the patient. This type of apparatus has also been used to detect the position of a metal needle which serves as a location reference after it has been inserted into a patient during a surgical operation. This catheter can be dangerous, however, because it carries electricity into the body. Many internal organs, including the heart and the brain, can be damaged by stray electrical currents. Another unattractive characteristic of this device is its high cost. Since each catheter and the complicated electronic transducer which it contains are used only once and are then discarded, this device is very expensive to use.
The problem of providing an accurate and reliable method of catheter visualization that avoids the danger of introducing stray electrical currents into the body has presented a major challenge to designers in the field of medical imaging. The development of a method and an apparatus that determines the precise location of such an instrument within the body would constitute a major technological advance. The enhanced performance that could be achieved using such an innovative system would satisfy a long felt need within the medical profession and would enable physicians to better care for their patients.